Understand what you are doing. Have a *sense* of what is right and wrong, which of course, is gained by experience.
The best thing one can do is just search around for good resources. Whenever you find a question that you can't do, note it down. These are the kind of questions that you should tackle. Once you get it, you will learn far more than from a simple chain-rule/quotient/composite function question.
For the most part, just be organised (wow... this is being really hypocrictical of myself.... but I realised this afterwards with hindsight.) You finish the course with a month or two in your pocket. What you should have done during the year is do some revision, so that in this month 2 weeks isn't devoted to relearning BUT TO ACTUALLY DOING EXAMS!!
There is however, a HUGE CBF factor to overcome. Once over this hurdle, it shouldn't be to hard to do.
Also, with formulas, look for patterns. This helps. Loads.